Gas fluidization of a 0.300 kg bed of silica powder and of a 0.225 kg bed of potato starch powder has been studied in an 85 mm ID mechanically vibrated column. The effect of frequencies between 15 and 150 Hz has been explored at a relative acceleration level of a/g = 2. Fixing the frequency at 120 Hz for silica and 70 Hz for potato starch, the effect of acceleration level has been studied between a/g = 2 and a/g = 10. The aggregative behavior of the powders has been highlighted, and a model procedure is proposed to predict the aggregate size from the measurement of powder flow properties with conventional shear testers. It has been assumed that the aggregate size adjusts to the value that is sufficient to detach the aggregate under the effect of the inertia introduced by the acceleration due to mechanical vibrations. The correctness of this assumption has been verified by estimating the aggregate size using the Ergun equation under conditions in which fluidization can be considered homogeneous. (C) 2012 Elsevier B.V. All rights reserved.